The invention relates to a beam generating system formed of a beam shaping electrode and a dispenser cathode supported therein and having an emission disc at its end face.
A beam generating system comprising a beam shaping electrode and a dispenser cathode which is cylindrical in shape and comprises an end emission face formed by a porous member is known for electron beam tubes from German Letters Patent 19 63 333, corresponding to U.S. Pat. No. 3,681,641, incorporated herein by reference.
Attempts have also been made to achieve a constant position of the dispenser cathode in a Wehnelt cylinder employed as a beam shaping electrode at various operating temperatures by means of suitable material selection or material combinations of the fastening films which reside axially in the system.
The axial fastening elements of the dispenser cathode in the Wehnelt cylinder which have been employed up to now give rise to positional changes of the dispenser cathode in the Wehnelt cylinder at different ambient temperatures and thus produce a beam defocussing.